Sunday, December 18, 2011

I've have one of these neat TI Beagleboard for a couple years, have not used it for a while. TI recently released a new hardware implementation of this family called the Beaglebone. This device looks to be more useable for hardware interfacing, so I picked up a couple to explore. At USD 90, the price of the Beaglebone shows the continued downward price curve of powerful embedded hardware.

I dusted off the older Beagleboard to do some comparisons with the newer Beaglebone hardware. So first off I decided to get the distro version as close as possible. Angstrom appears to be most used and updated distro for the family, but the Android folks look to be getting some steam up.

Here are my notes on getting the most current Angstrom distro running on the Beagleboard.

The one big gotcha that may trip up forever n00b's like me was the change of the TTY port naming conventions. The correct port name for the serial port on the Beagleboard is:

ttyO2

that is a capital OOOOOO as in Oscar not a zero!

After Linux kernel version 2.6.36 the naming convention appears to have moved from:

ttySx

--to--

ttyOx

I'm sure there is a really good reason to slipstream this change in, but not only is it not clearly announced / documented around the various Linux and embedded internet resources [one of those "weed 'em out events perhaps?"] but using the capital 'O' character seems to be making for more opportunities for mistakes by confusing it with the number zero '0'.

The standard instructions to create a SD card with the two partitions containing the u-Boot and linux kernel on the first FAT partition and the remaining core Linux core OS files on the second [one of several types] Linux/Unix formatted partition is straight forward and does not vary from prior configs.

The main two changes to get the console output and the a serial terminal login prompt are as follows:

1) change the Linux bootargs console value to be:

console=ttyO2

REMEMBER THAT IS A CAPITAL O NOT A ZERO!

my basic u-Boot environment variable 'bootargs' is as follows:

bootargs=console=ttyO2,115200n8 root=/dev/mmcblk0p2 rw rootwait

2) Before you put the SD card into the Beagleboard, or after via the X Window session that comes up by default, edit the inittab file in /etc and change the following line from:

S:2345:respawn:/sbin/getty 115200 ttyS2

--to--

S:2345:respawn:/sbin/getty 115200 ttyO2

this will give you a login prompt on the Beagleboard's serial port.

Results and experiences to date.

I am still testing the 3.x kernel on the Beagleboard, so far so good. The serial port might be exhibiting some slow down after a the machine is up for a while. I need to get more data on this. Unfortunately, most of my focus is on the new Beaglebone, so the '..board' is getting the 'old dog' treatment. The puppy is the center of attention.

I updated the two boot modules of the Beagleboard to what I believe is the most current version. You get these by putting the MLO and u-boot.bin files on the FAT boot partition when you download the latest build of Angstrom. There are couple of thinks to be aware of with these upgrades. The version of these files that are in the flash memory of the Beagleboard are the older version until you use the u-boot commands to re-flash them. The instructions to do this are straight forward and worked fine. The 'gotcha' here comes in that the commands in u-boot have changed considerable and the boot scripts are stored as environment variables in the flash. So your old boot scripts will work with with your old SD cards and when you boot these files from flash [by removing the SD card or holding down the 'user' button during power up]. However, when you boot with the newer u-boot, thinks quit working. And, unfortunately, it appears to be even worse than the new versions don't work the same as to older version. It appears that the documentation and perhaps some of the commands do not work as documented that you will find on the 'help' sites on the web. I have not got my arms around these 'additional' issue yet so take this with a grain of salt, but do watch carefully as commands run. One example of what I am talking about is the 'mmc' command family to work with the SD card. There is much discussion of a 'mmcinit' command, but I could not find that command anywhere. What I did find is that before reading from the SD card, it is a good idea to do a 'mmc reset' each time before loading a file or doing a directory of the mmc. Below is my before and simple v1 'after' environments:

-- before version of environment variables that booted a October 2009 Angstrom Linux --

Good basic setup instruction of the Beagleboard. Old so it does not address the problems I highlighted above, but still a good anchor to go back to:

http://www.ibm.com/developerworks/linux/library/l-beagle-board/

Beagleboard web site:

http://beagleboard.org/

Angstrom Linux for Beagleboard latest version. NOTE: go to the Amazon AWS mirror of this web site to get much faster download of files:

http://www.angstrom-distribution.org/demo/beagleboard/

Summary...

Pretty frustrating waste of time I had as a n00b here because the 'in the know' folks that are maintaining this stuff did not take five minutes to document some of the rather major changes. Glad I have it working! The Beagleboard and Beaglebone are great training ground for the amazing world of embedded connected inexpensive devices we are moving to.